Method of cleaning an oven with internal air circulation

ABSTRACT

A self-cleaning oven is provided with a rack which is substantially closed at its sides, fully open at one end, and formed as a hood at the other end. A centrifugal fan is provided in the oven at the hood used to circulate air around and through the rack. An air inlet is provided in the oven wall that opens adjacent the fan intake. The oven is further provided with an outlet fitted with a catalytic afterburner. During heating of the oven to 400*-500* C. for cleaning, fresh air is drawn in through the inlet, circulated throughout the oven interior, and exhaust gases pass out through the afterburner.

United States Patent 151 3,669,090

Jung et a1. [451 June 13, 1972 METHOD OF CLEANING AN OVEN 3,384,0685/1968 Perry et a1 ..126/21 A W T N E N R CIRCULATION 2,846,961 8/1958Nelson ....126/2l A UX 3,121,158 2/1964 Hurko ..126/21 A UX [72]lnventors: Anton Ladislaus Jung, Am Gerichtskoppel f Harbor; ErhardLedwonv schlm' Pn'mary Examiner-Charles J. Myhre kenwleg 10, 6349Guntersdorf, both of Ao,ney Kar|F RoSS Germany 22 Filed: May 25, 1970 1ABSTRACT.

2 Appl. 40 12 A self-cleaning oven is provided with a rack which issubstantially closed at its sides, fully open at one end, and formed asa hood at the other end. A centrifugal fan is provided in the [30]Fore'gn Apphcmon Pnomy Data oven at the hood used to eirculate airaround and through the Aug. 18, 1969 Germany.....- ..P 19 41 935.3 rack-An air inlet is P' in the Oven Wall "131911695 jacent the fan intake.The oven is further provided with an 52 us. (:1. ..l26/21 A 1 outletfined with a catalytic afrerbumer- During heatingofrhe 51 CL 24 15/32oven to 400500 C. for cleaning, fresh air is drawn in 58 1 Field ofSearch 126 21, 21 A, 273 through the inlet, circulated throughout theoven interior, and

I I V exhaust gases pass out through the afterburner. 6 f [5 1 Re "ences9 Claims, 4 Drawing figures UNITED STATES PATENTS 3,437,085 4/1969 Perry..126/2l A 5 HA 8 GAS S UT 73 v 5 x u r E o 7 FEESH HIE IN OOOOOOOOOOOPATENTEDJuu 13 I972 L0. FIG. 3

- I XHAUYI' GASES OUT FRESH HIE IN OQOOOOQOOO Erhard Ledwon AttorneyMETHOD OF CLEANING AN OVEN WITH INTERNAL AIR CIRCULATION Y FIELD OF THEINVENTION The present invention relates to a method of cleaning an oven.

BACKGROUND OF THE INVENTION A self-cleaning oven differs from a normaloven in that it is extremely well insulated and can be heated toextremely high temperatures, e.'g., 400-500 C, to pyrolyticallydecompose any food residue in the oven. It is also known to provide incertain cases a catalytic afterburner on the oven to remove the morenoxious gases H CO)created during the pyrolytic decomposition of theresidue.

A considerable problem with such ovens is that it is virtuallyimpossible to clean them completely, since certain dead corners do notheat up 'sufficiently to become clean. One attempt to overcome thisdisadvantage has been to heat the oven so much that even the most'inaccesible nooks and crannies become sufficiently hot to destroy thefood particles adhering therein. Of course, such a method is costlybecause of the large'amount of energy required to create the additionalheat and the insulating problems this heat brings about.

OBJECTS OF THE INVENTION SUMMARY OF THE INVENTION The above objects areobtained according to the present invention by a self-cleaning thawing,baking, or roasting oven which is provided withblower means in the formof a centrifugal fan that serves to circulate air throughout the ovenduring the self-cleaning thereof. The oven is provided with an inletopening adjacent the fan intake, i.e., near the. center of the fan, andan outlet which is combined with a small catalytic afterburner. Freshair 'is sucked in through the inlet by the fan and passed over a heatingelement whence it flows around the oven rack and finally a part of theheated air exits through the outlet. The fan circulates the hot air inevery portion of the oven, so that it is thoroughly cleaned, while thefan effects a very good mixing of the air so that an excellent primaryoxidation of the'often noxious combustion products is attained.

It is indeed a surprising discovery, in accordance with the principlesof the present invention, that the recirculation of air within afoodtreatment chamber,accompanied by heating to pyrolytic decompositiontemperature of the food residues, will thoroughly clean even the mostcomplex chambers or ovens. Preferably, the gas circulation ratepermitted is in excess of the volumetric capacity of the chamber perminute and can range up to times the volumetric capacity per minute,although improvement has been found even with circulation rates as lowas one tenth the volumetric capacity of the furnace per minute. While itappears that the velocity of the air stream within the chamber is not assignificant, it nevertheless has been discovered that the fan should bedriven at a speed such that the Reynolds number is exceeded at mostplaces within the chamber. Furthermore, it is advantageous to admit aquantity of air per minute, for catalytic combination with gasified andpyrolytically decomposed food residues, which is less than thevolumetric capacity of the chamber although air in an amount equal tothe volumetric capacity of the chamber per minute or exceeding thisamount may be admitted with diminished results. In all cases, thecatalytic afterburner, which may be provided with an auxiliary source ofair independent of that admitted to the food-treatment chamber, shouldhave a conversion capacity exceeding the maximum throughflow which canbe controlled to equal the volumetric flow of air into the chamber perunit time. Hence, again, the

capacity per minute of the catalytic afterbumer may be less than thevolume of the chamber per minute. The heating means within the chamber,of course, should be dimensioned to enable the recirculated gases to bebrought to a temperature of 400-500 C rapidly, i.e., within a fewminutes, while care should be taken to circulate the gases from the fanoutwardly into contact with the heating elements and thence along theouter walls of the food-treatment chamber.

DESCRIPTION OF THE DRAWING The above and other objects, features, andadvantages will become apparent from the following description,reference being made to the accompanying drawing, in which:

FIG. I is a longitudinal section through a first embodiment of the ovenaccording to the invention; 7

FIG. 2 is a view similar to FIG. 1 showing a second embodiment of thepresent invention; I

FIG. 3 is a section taken along line III-III of FIG. 2; and

FIG. 4 is a view similar to FIG. 3 showing a third embodiment of thepresent invention.

SPECIFIC DESCRIPTION There is shown in FIG. 1 an oven 7 having at oneend a door 8 hinged at 9 and at the other end a centrifugal fan 2mounted on the shaft 1a of a motor 1 which is mounted on the outside ofthe oven 7 via a flange lb and is connected to a source of power 10(FIG. 2). Any one of the centrifugal fans described on pages 6-20 f.f.of PERRYS CHEMICAL ENGINEERS HANDBOOK of John H.Perry (McGraw-Hill1963), can be used here, it only being important that the fan have anaxial intake and radial output.

Adjacent the output of this fan 2 is a heating element 3 in the form oftwo annular burners having openings 30 (FIG. 3) connected through aconduit 3b to a gas source 3a (FIG. 2). An inlet pipe 4 opens justadjacent the shaft 1a so that fresh air can be drawn into the oven bythe Venturi effect. This air,

heated to around 450 C, is circulated around an oven rack adapted tocarry trays of food to be cooked. It is constantly circulated with asmall portion being exhausted through a catalytic afterburner 5 mountedatop the oven.

FIGS. 2 and 3 show a rack 6a in greater detail. It is fitted withL-brackets 10 which serve to support the edges of foodholding grates ortrays and is supported on legs 15. Its side walls are formed withventilating holes 16 and its top is open, struts l3 spanning it. At theend adjacent the door 8 the rack 6a is fully open, while at its oppositeend it tapers and is formed with a port opening into the center of thefan 2, so that this fan 2 draws air, as shown by the arrows, through therack and then forces it outwardly around this rack. The chamber of theoven is tapered at 17 to aid this air flow.

A valve 18 can be provided in the inlet pipe 4, and the outlet 5 can becoupled to an outdoor vent.

The embodiment of FIG. 4 is identical to that of FIGS. 2 and 3 exceptthat a rack 6b is provided which is closed at its top 19 and sides andis, therefore, only open at its two ends. In this manner, a very directair current is created which flows all around the rack 6b and thenthrough its center, as an inverting toroid. Of course, under anyconditions the hood-like shape of the end of the rack adjacent the fan 2causesa similar air flow, even when the top of the rack is open and thesides perforated, as shown in FIGS. 1-3.

EXAMPLE A roasting oven as shown in the drawing, i.e., wherein theheight and width are approximately equal but the depth is about threetimes greater than height or width, with a volume of about 50 m isoperated in the conventional manner until substantial accumulations ofgrease, soot and food deposits are found over substantially all of theinterior surfaces. After the last cooking cycle, the oven is closed,brought to a temperature of 500 C by electric heaters and, using thecentrifugal fan illustrated, air is circulated at a rate of about m /min(STP); the fan has a specific speed N. 1,000. Within a few minutes afterthe oven is brought to the indicated temperature, it is observed thatpyrolytic decomposition occurs throughout the interior with gasificationof the pyrolyticdecomposition products except for a trivial quantity ofash (substantially pure carbon) which is entrained as particulate matterwith the effluent high-speed air stream. Fresh air is admitted (byaspiration via the fan) at a rate of about 5-10 m lmin (STP) whileexhaust gases emerge at a corresponding rate. The afterbumer is of thecatalytic type and charged with a wire mesh coated with nickel-platinumreformation catalysts of conventional composition and adapted tocatalytically convert up to 20 m /min of oxidizable matter and thecorresponding quantity of oxygen to H 0 and CO A thoroughly clean ovenis obtained after a period of several minutes whereas traces ofcarbonaceous matter remain in the oven without recirculation even whenthe latter is heated substantially higher and the cleaning operation ispermitted to continue for longer periods.

We claim:

1. A method of cleaning an elongated cooking chamber having alongitudinal horizontal axis and a rear wall, said method comprising thesteps of:

drawing gases along the horizontal axis of said chamber toward the rearwall thereof and expelling said gases uniformly radially outwardly insaid chamber from said axis adjacent said wall to circulate said gasesin said chamber in contact with all internal surfaces thereof;

introducing into said chamber an oxygen-containing gas at a locationadjacent said rear wall and offset from said axis; removing an exhaustgas from said chamber through an outlet remote from said rear wall;

catalytically afterbuming said exhaust gas at said outlet; and

heating said gas adjacent said rear wall in a ring all around said axisto a temperature sufficiently elevated to pyrolitically decompose foodresidue on said surfaces of said chamber.

2. The method defined in claim I wherein said chamber is provided with arack, said gases being blown around said rack.

3. The method defined in claim 1 wherein said oxygen-containing gas isintroduced into said chamber by being drawn in.

4. The method defined in claim 1 wherein said oven is heated adjacentsaid rear wall by passing it in contact with heating elements at atemperature of 400 to 500 C.

5. The method defined in claim 4 wherein the gas in said chamber iscirculated at a rate exceeding the volume of said oven per minute.

6. The method defined in claim 5, further comprising the step ofadmitting air to said oven substantially at the rate at which exhaustgas is removed therefrom and less than the volume of said oven perminute to constitute said oxygen-containing gas.

7. The method defined in claim 6 wherein said air is aspirated into saidoven by the circulation of the gases at said rear wall.

8. The method defined in claim 7 wherein said outlet is formed along awall of said chamber other other than said rear wall.

9. The method defined in claim 8 wherein the oven is provided with arack and the gases pass around said rack upon movement toward said rearwall.

1. A method of cleaning an elongated cooking chamber having alongitudinal horizontal axis and a rear wall, said method comprising thesteps of: drawing gases along the horizontal axis of said chamber towardthe rear wall thereof and expelling said gases uniformly radiallyoutwardly in said chamber from said axis adjacent said wall to circulatesaid gases in said chamber in contact with all internal surfacesthereof; introducing into said chamber an oxygen-containing gas at alocation adjacent said rear wall and offset from said axis; removing anexhaust gas from said chamber through an outlet remote from said rearwall; catalytically afterburning said exhaust gas at said outlet; andheating said gas adjacent said rear wall in a ring all around said axisto a temperature sufficiently elevated to pyrolitically decompose foodresidue on said surfaces of said chamber.
 2. The method defined in claim1 wherein said chamber is provided with a rack, said gases being blownaround said rack.
 3. The method defined in claim 1 wherein saidoxygen-containing gas is introduced into said chamber by being drawn in.4. The method defined in claim 1 wherein said oven is heated adjacentsaid rear wall by passing it in contact with heating elements at atemperature of 400* to 500* C.
 5. The method defined in claim 4 whereinthe gas in said chamber is circulated at a rate exceeding the volume ofsaid oven per minute.
 6. The method defined in claim 5, furthercomprising the step of admitting air to said oven substantially at therate at which exhaust gas is removed therefrom and less than the volumeof said oven per minute to constitute said oxygen-containing gas.
 7. Themethod defiNed in claim 6 wherein said air is aspirated into said ovenby the circulation of the gases at said rear wall.
 8. The method definedin claim 7 wherein said outlet is formed along a wall of said chamberother other than said rear wall.
 9. The method defined in claim 8wherein the oven is provided with a rack and the gases pass around saidrack upon movement toward said rear wall.